1. Field of the Invention
The present invention relates to deblocking of compressed images, and more particularly, to a method of and apparatus for deblocking Block Discrete Cosine Transform compressed images based on an edge flow-directed filter and curvelet transform.
2. Description of Related Art
Block Discrete Cosine Transform (BDCT) is widely used to define a standard for encoding still images such as Joint Photographic Experts Group (JPEG), Motion Picture Experts Group (MPEG), H.263, etc., and motion pictures. In BDCT, an image is divided into blocks, which are separately compressed irrespective of correlations between the blocks. In this regard, since a Discrete Cosine Transform (DCT) is used to compress an 8x8 block or 16x16 block, block compression at a low bit rate results in a remarkable discontinuity across block boundaries, which is called a blocking artifact.
Various techniques for removing blocking artifacts have been studied. One such technique is post-processing, which processes an image after a decoder regardless of a compressor/decompressor (codec) structure, is divided into an image reinforcement method and image restoration method.
The image reinforcement method removes blocking artifacts by properly filtering block boundaries using a filter. The image restoration method restores a decoded image using a Maximum A Posteriori (MAP), or a Projection Onto Convex Sets (POCS).
Some efficient deblocking methods using wavelet representation have been proposed. However, these methods may not be suitable for images containing a large portion of texture. An adaptive method for determining the soft threshold and different threshold values and strategies has been used for determining the wavelet coefficients at different high frequency subbands, but it had less peak signal-to-noise ratio (PSNR) improvements compared to a POCS-based method. And it also shows that compactly supported wavelets can lead to many visual artifacts when used in conjunction with nonlinear processing, particularly for decimated wavelet used at critical sampling.